The present invention relates generally to optical devices, and more particularly, to a coating for an optical element such as a window over the illuminating or illuminated surface of an optical device.
Various light transmissive coatings have been used to protect optical elements. For example, the optical element might be a window that covers an optical device that emits or receives radiation. A coating on the window might provide some desired characteristic to the cover. Two examples of factors that enter into the selection of material for such coatings are the type of incident radiation on the device, or emitted radiation from the device, and the environment in which the device will be used.
An example of a coated window for an optical device is described in U.S. Pat. No. 5,324,856, entitled xe2x80x9cPolymeric Infrared Optical Protective Coatingxe2x80x9d, assigned to Texas Instruments Incorporated. It describes the use of various polymeric coatings on a window to provide a low hardness and high strength cover for the device. The polymers of choice provide infrared transmissivity in a desired wavelength range.
One aspect of the invention is an optically transmissive cover for an optical device. The cover is comprised of a window having an inner surface and an outer surface with respect to the optical device. A coating on at least one of the window""s surfaces is made from a halogenated material. The coating is deposited using a deposition process, such as xe2x80x9csemiconductor deposition processesxe2x80x9d as defined herein, and such that the halogenated material is chemically bonded to the window. An example of a suitable halogenated material is a perfluorinated material, which imparts a hydrophobic quality to the cover.
In addition to use of the cover with optical devices that benefit from the hydrophobic quality of the cover, a particular application of the cover is for digital micro-mechanical (DMD) devices. In the case of a DMD, which has micro-mechanical elements housed under the cover, the coating can be made from the same material as the material used for lubricating or passivating surfaces of the micro-mechanical elements. The coating is placed on the inner surface of the window. It then prevents the inner surface of the window from being a chemically active sink for the lubrication or passivation material, as well as provides a source of molecules that migrate to the surfaces requiring lubrication or passivation.